Calculate Force for Beam Shear Failure

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Discussion Overview

The discussion revolves around calculating the force necessary to cause shear failure in a component made of 303 stainless steel, specifically focusing on a part from an ice maker that failed after prolonged use. The inquiry includes considerations of material properties, failure modes, and the conditions under which the failure occurred.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant seeks assistance in calculating the force required for shear failure, providing details about the component's dimensions and material.
  • Another participant questions the temperature at which the component failed, suggesting that temperature may influence material properties.
  • A later reply suggests using the equation for shear stress (Force/area) to estimate the failure load, noting that this approach may only provide an upper bound due to complex forces on gear teeth and stress concentrations.
  • Participants discuss the appearance of the fracture surface, with one describing it as part crystalline and part dull, indicating different failure modes (brittle and ductile).
  • One participant identifies the crystalline part as indicative of brittle failure, while the dull part suggests ductile failure.

Areas of Agreement / Disagreement

Participants express varying views on the complexity of the forces involved in gear teeth and the interpretation of the fracture surface, indicating that the discussion remains unresolved regarding the exact calculations and implications of the failure.

Contextual Notes

Participants have not reached a consensus on the appropriate method for calculating the force or the implications of the observed fracture characteristics. The discussion highlights the need for further exploration of material properties and failure analysis.

Hockeyguy2026
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I started a new job two weeks ago and I've been out of school for twenty years and have not used strength of materials knowlegde since. I had a part fail in the lab and I would like to calculate the force that would have been necessary to cause the shear failure. I have simplified the problem to a 1/2" tall tooth with a cross section area of .125". The material is 303 stainless steel. Can anyone help me with the equation to find this force. I understand that the part failure was caused by repeative stress and not a blunt force but my first step is to find that blunt force value.
 
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What temperature was the component running at at failure?
 
The temperature was below freezing - approx. -5C. The failed compent was from an ice maker.
 
OK so standard quoted materials properties would apply.

Shear stress = Force/area

So you can calculate a coarse failure load by multiplying the shear stength of your steel by the 1/8 sq inch.

However the forces on gear teeth are much more complex so this will only give you an upper bound. There are significant stress concentrations depending upon the shape of the teeth.

Also, what did the fracture surface look like? Can you describe it?
Was it crystalline and shiny or dull and smooth? or was it part crystalline and part dull?
 
The failure looks part crystalline and part dull. The part that broke off is a stream divider that changes the flow of ice from an evaporator to a nozzle that pushes the ice through a tube. The part failed after many months of 24/7 operation.
 
The crystalline part is brittle failure, the dull part ductile failure.
 

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